Morphological and Physiological Adaptations to Light Stress in Different Impatiens New Guinea Hybrids

Impatiens New Guinea hybrids are sensitive to high light conditions, high temperature and low moisture. Consequently, abiotic stress tolerance is one of the main targets of breeders. The aim of this investigation was to characterize the light stress reaction at morphological and physiological level of five Impatiens cultivars and to evaluate chlorophyll fluorescence measurements as a standardized light stress screening method. To produce plants with a higher light sensitivity the cultivars were grown under reduced light intensity (70% shading). Histological study showed that the leaves developed under high light conditions have more densely packed palisade parenchyma and more chloroplasts compared to the leaves developed in low light conditions. After 8 weeks of pre-treatment with different light conditions, plants were transferred to different light stress treatments: outside in full sun radiation, under UV-permeable foil, and under light protection by UV-impermeable foil. After 12 h of full sun radiation, several sun-exposed leaves were already damaged. In addition, the light stress reaction of the plants was evaluated by measuring the chlorophyll fluorescence and documenting leaf damage daily. Within seven days of light stress treatment, the plants subjected to the low light pretreatment had a significantly higher stress reaction than the plants subjected to the high light pre-treatment. However, these reactions were not confirmed by the chlorophyll fluorescence measurements. No significant differences between cultivars subjected to the low light pre-treatment were seen and the results demonstrated that the conditions of plant cultivation have more influence on the light stress adaptation than the genotype.